The long-term objective of this study is to understand the basic cellular mechanisms of sensory transduction in the inner ear. The primary immediate objective is to investigate whether or not auditory hair cells can actively protect themselves from overstimulation by clumping together their longest stereocilia. Stereocilia clumping during the period of tempory threshold elevation following exposure to loud noise has been observed in preliminary studies. The specific aims of this proposal are to test whether or not: 1) stereocilia recover morphologically on the same time scale as the ear recovers functionally, 2) temporary threshold shift (TTS) clumping differs from the stereociliary pathologies associated with permanent threshold shifts, 3) the phenomenon is physiologically vulnerable, 4) TTS can be induced by electrical stimulation, 5) stereocilia can be induced to clump by direct electrical stimulation, 6) the phenomenon occurs in mammalian auditory hair cells, and 7) there are ultrastructural changes in the stereocilia during TTS.